1. Field of the Invention
Embodiments of the present invention relate to deposition methods for forming thin metal films, such as copper films, on substrates for use in manufacturing semiconductor devices, flat-panel display devices, and other electronic devices.
2. Description of the Related Art
In the field of semiconductor processing, flat-panel display processing or other electronic device processing, chemical vapor deposition has played an important role in forming films on substrates. As the geometries of electronic devices continue to shrink and the density of devices continues to increase, the size and aspect ratio of the features are becoming more aggressive, e.g., feature sizes of 0.07 microns and aspect ratios of 10 or greater are being considered. Accordingly, conformal deposition of materials to form these devices is becoming increasingly important.
While conventional chemical vapor deposition has proved successful for device geometries and aspect ratios up to 0.15 microns, the more aggressive device geometries require new, innovative deposition techniques. One technique which is receiving considerable attention is rapid cycle (pulsed) CVD or atomic layer deposition. In this scheme, reactants are sequentially introduced into a processing chamber where each reactant adsorbs onto the surface of the substrate where a surface reaction occurs. A purge step is typically carried out between the delivery of each reactant gas. The purge step may be a continuous purge with the reactant gases or a pulse purge between the delivery of the reactant gases.
Materials which are useful in forming conductive devices in semiconductor as well as flat-panel display processing include copper, titanium, tantalum, aluminum, tungsten, and nitrides of the refractory metals.
Chemical vapor deposition of copper has been a difficult process to incorporate into commercial production. One problem has been the difficulty in determining or finding a suitable precursor. Existing copper precursors have contained additional elements such as fluorine that can impede their use as a suitable precursor for electronic applications, or have a chemical composition that is not suited for large scale production of electronic components. For example, some potential source reagents are solids that are amenable to sublimation for gas-phase transport into the processing chamber, however the sublimation temperature may be very close to the decomposition temperature. Accordingly, the reagent may begin to decompose in transit. As a result, accurate delivery of reagent is impeded and additional chamber cleaning would be required.
Thermal decomposition of organometallic source reagents is a particularly attractive method for forming metal films because it is readily scaled up to production runs and because the electronics industry has a wide experience and an established equipment base in the use of vaporization and decomposition technology.
Semiconductor processing requires source reagents that are sufficiently volatile to permit their gas phase transport into the processing chamber. The source reagent must decompose in the chamber to deposit only the desired element(s) at the desired growth temperature on the substrate. Premature gas phase reactions are desirably avoided, and it generally is desired to controllably deliver source reagents into the reactor to effect correspondingly close control of film stoichiometry.
Therefore, there is a need for a deposition process and a copper precursor which can reliably form copper layers in very small aggressive geometries.
Embodiments of the present invention provide deposition processes in which nitrogen containing analogs of Copper II xcex2-diketonates, are reduced using moderate reducing agents. The nitrogen containing analogs replace xe2x80x94Oxe2x80x94 with xe2x80x94N(Rxe2x80x3)xe2x80x94 wherein Rxe2x80x3 is an alkyl group having from one to four carbon atoms. Replacement of each xe2x80x94Oxe2x80x94 is preferred although replacement of one xe2x80x94Oxe2x80x94 per cyclic ring is sufficient to improve stability of the copper source reagents. The nitrogen containing analogs are preferably separated from solvents and excess ligands by sublimation. The processes are performed at chamber pressures in the range of about 0.1 to about 10 Torr at substrate temperatures of about 50 to about 200xc2x0 C.
In one embodiment, the copper layer of the present invention is deposited by the cyclical deposition technique using the nitrogen containing analogs of Copper II xcex2-diketonates and the reducing agent to provide a copper layer that may contain carbon, nitrogen, and oxygen constituents. The copper layer adheres well to copper barrier layers.